1. Field of the Invention
The present invention relates to a pneumatic tire in which the steering stability can be improved while maintaining the wet performance.
2. Description of the Related At
As shown in FIG. 5, JP2008-6987A1 discloses a pneumatic tire with a tread pattern to improve the steering stability while maintaining the wet performance.
The tire comprises a tread portion provided with a pair of circumferentially extending center main grooves (a) disposed both sides of the tire equator (Co), and a pair of circumferentially extending shoulder main grooves (b) disposed both sides of each center main groove (a) to define the tread portion into five ribs which include a center rib r1, a pair of middle ribs r2i, r2o, and a pair of shoulder ribs r3i, r3o. Center main grooves (a) include an inboard center main groove (ai) and an outboard center main groove (ao). The center rib (r1) is provided with a plurality of curved grooves y1 extending from the inboard center main groove (ai) beyond the tire equator (Co) and turning back toward the inboard center main groove (ai) without reaching the outboard center main groove (ao). Curved groove y1 are crossing each other on the tire equator Co, and thereby the center rib r1 is separated into two parts with an outboard part (e) continuously extending in the circumferential direction of the tire and an inboard inner block row including a plurality of blocks (f) divided by curved grooves y1 and y1. The middle ribs r2i provided in the inboard side is formed as a block row with a plurality of blocks (h) divided by the lateral grooves y2i, and the shoulder rib r3i provided in the inboard side is also formed as a block row with a plurality of blocks (i) divided by the lateral grooves y3i. The shoulder rib r3o is provided in the outboard side is also formed as a block row with a plurality of blocks (j) divided by the lateral grooves y3o. In the tire, curved grooves y1, lateral grooves y2 and lateral grooves y3 are disposed so that each of one y1, y2 and y3 is smoothly continued through main grooves ai and bi to be formed as a long one lateral groove Y, and thereby the inboard tread portion can improve the wet performance. However, the wet performance in the outboard middle portion r2o is not enough, and especially, the so called lateral hydro performance, which is a wet performance during cornering, is not enough. The pattern rigidity of the tire is also not enough. Accordingly, there is room for improvement as to the wet performance as well as the steering stability.